I do have a few general concerns whenever a home hobbyist is considering using a nano tank or biocube for their seahorses. These can be summarized as follows:
(1) Powerful water flow – the strong, vigorous water movement produced by the pumps for a nano tank may be too overpowering for the limited swimming ability of the seahorses.
(2) High-Intensity Lighting – metal halides and other high-intensity lighting systems are not a good choice for a seahorse tank. Colorful seahorses will produce excess melanin and darken when exposed to high-intensity lighting, so it would be a shame to display Sunbursts under metal halides only to see them turned dark brown or black in coloration as a result. More importantly, metal halides throw off a lot of waste heat and may contribute to overheating, with unfortunate consequences.
(3) Overheating – many nano tanks and reef tanks tend to run on the warm side, which is often a consequence of the waste heat given off by powerful submersible pumps and high-intensity lighting. That’s not a good situation for seahorses, since Ocean Rider Mustangs and Sunbursts are most comfortable with stable water temperatures in the range of 72°F-77°F, and they may begin to experience heat stress and associated health problem when the water temperature approaches 80°F or above for any length of time.
Nano tanks and biocubes tend to have problems in these three areas because they are designed primarily with the reef keeper in mind, and are often equipped with the sort of high-intensity lighting stony corals require in order to thrive, as well as powerful water pumps that can provide the strong water flow the stony corals are accustomed to and often require for their long-term health.
As a result, the nano tanks and biocubes often require some significant modifications in order to make them suitable for seahorses. The spray bar return that you used for the closed nano tank is a great way to manage the water circulation, Tammy! The spray bar does a wonderful job of softening and diffusing the output from the water pumps, so that it produces good water circulation without being too overpowering for the seahorses, allowing you to use powerful pumps that provide a much higher turnover rate that would normally be possible.
At the same time, the spray bar return also increases surface agitation and facilitates efficient gas exchange at the air/water interface, which is very desirable since it keeps the dissolved oxygen levels in the aquarium nice and high and keeps the dissolved carbon dioxide levels nice and low. This makes it easier to maintain stable pH in the normal range, as well as making it easier for the seahorses to breathe using their primitive tufted gills.
If you can manage the water circulation in the new nano tank much the same way, using a spray bar return, then I don’t think you’ll have any problems with either the water movement or the gas exchange in the new aquarium, Tammy.
If necessary, you can always replace high-intensity lighting with one of the new LED light fixtures instead, or even the right combination of T5 fluorescent tubes, which will help to avoid any problems with overheating as well as helping to assure that your seahorses will look their best and brightest.
I do believe it is helpful to have a more open top on a nano tank, but not so much for the sake of gas exchange, rather more to help prevent any potential problems with overheating. In the closed nano tanks, the airspace beneath the cover traps a lot of heat, which again is often released as waste heat from high-intensity lighting or from the high-powered submersed circulation pumps, which transfer a lot of heat to the aquarium water, which in turn is eventually transferred to the air gap at the top of the tank beneath the cover. As you know, air is a wonderful insulator of heat, so a closed aquarium with a tightly fitting cover or hood often runs much hotter than a similar aquarium with a more open top, Tammy.
In short, one advantage of an aquarium with an open top is that it allows the heat to be released and dispersed into atmosphere, so that the water temperature will remain closer to the ambient air temperature, thereby helping to prevent overheating of the aquarium water in the process.
In my experience, there are only two minor drawbacks to a seahorse tank with an open top. The first disadvantage is that the tank with the open top will experience more rapid evaporation, and you will therefore need to be more diligent about topping off the tank with purified freshwater in order to maintain the proper specific gravity. But that’s easy enough to accomplish, so that’s not really a significant drawback.
The more important disadvantage of having a seahorse tank with an open top is that it will limit potential tankmates for your seahorses to aquarium fish that are not jumpers. Of course, there is no danger that a seahorse might leap out of a tank with an open top, but that can be problematic for some of the other compatible companion fish that are inclined to jump if they are startled or feel threatened…
In other words, Tammy, I don’t see any real serious problems in shifting from a nano tank with a closed top to a new tank with a more open top instead. The open top will be more beneficial in terms of preventing overheating and helping to assure efficient gas exchange at the air/water interface, and you will just need to be selective when choosing the companions for your seahorses so that you don’t include any fish that are jumpers.
Best wishes with all your fishes, Tammy!
Pete Giwojna, Ocean Rider Tech Support